Accidents involving the introduction of air emboli in the coronary or cerebral circulation paths through cardiotomy or pump oxygenator procedures can result in devastating injury. Proposed here is a non-invasive mechanism for quickly and accurately detecting the presence of air emboli in the infusion path and thus help reduce the risk of such procedures. The goal of the proposed program is to adapt an existing microwave radiometry system with appropriate target antennas to "see" air emboli traveling through plastic or glass tubing used to deliver fluid/blood to a patient. This radiometric technique monitors the noise level emitted by fluid flowing through a transducer containing a microwave antenna. Since the noise level of the target is a function of its dielectric properties, this system will in effect monitor the fluid-to-air ratio of the media within the boresight of the antenna. Using this principle, transducers and associated circuitry will be developed to optimally detect the presence of even very small air emboli within infusion lines. The sensitivity and specificity of the system will be determined as related to parameters such as tubing size, fluid type, fluid flow rate, fluid line pressure, fluid temperature and air bubble size.